Upgrade to Penpal version 3.1.2

The penpal documentation advises to create an iframe element first and add the sandbox attribute before connecting to it. To pass the existing iframe to Penpal is not yet possible in the version we currently use (3.0.3). We should upgrade to version 3.1.2 for this. We also benefit from some bugfixes.

In the channel manager /frontend-ng/src/app/services/openui.service.js should be updated to match the recommendation from penpal.

Also the ui-extension library must use this latest version.

https://www.npmjs.com/package/penpal